1. Field of the Invention
This invention concerns a method of operating an air-supplied type coating booth and, more specifically, it relates to a method of operating an air-supplied type coating booth in which conditioned air supplied from a supply blower to a plenum chamber is enforced through a filter to the inside of a tunnel-shaped coating booth at a predetermined flow velocity and the air in the coating booth is drawn to exhaust together with coating mists, evaporated organic solvents and the likes by an exhaust blower to the beneath of a booth floor.
2. Description of the Prior Art
In a relatively large-scaled air-supplied type coating booth for coating articles, e.g., car bodies conveyed successively on a conveyor, conditioned air supplied from a supply blower to a plenum chamber is enforced through a filter to the inside of the coating booth, caused to flow downwardly at a predetermined flow velocity in the coating booth and then drawn to exhaust together with coating mists, evaporated organic solvents and the likes to the beneath of a booth floor. This downwarded air flow can prevent the coating mists, dusts or the likes that would otherwise give undesired effects on coated films from scattering and drifting upwardly in the coating booth, thereby maintaining a desirable coating quality, as well as keeping the health of operators who make preparation for the coating work or conduct manual spray coating in the coating booth.
In this case, the flow velocity of the conditioned air enforced through the filter to the inside of the coating booth is usually set to about 0.2-0.5 m/sec.
However, since the filter used for enforcing the conditioned air supplied to the plenum chamber to the inside of the coating booth is often clogged with the elapse of time by dusts or the likes and the flow velocity of the conditioned air enforced through the filter to the inside of the coating booth is gradually lowered.
If the flow velocity of the conditioned air enforced into the coating booth is reduced with the elapse of time, coating mists, evaporated organic solvents, dusts or the likes resulted upon spray coating drift at the inside of the coating booth to degrade the coating quality and, at the same time, worsen the working circumstances.
Further, the balance between the flow rate of the air supplied from the supply blower and that of the exhaust discharged from the exhaust blower is lost thus leading to the intrusion of external air through the inlet and the exit of the coating booth to degrade the coating quality.
Such disadvantages may be overcome by the frequent exchange of the filter but the replacing work is extremely troublesome.
In view of the above, it has been attempted in recent years to measure the flow velocity of air supplied into the coating booth and control the number of rotation of the air supply blower depending on the measured value. However, since the flow velocity of air at the lower surface of the filter is as low as from 0.2 to 0.5 m/sec and there are also involved various factors of external disturbances resulted from the air conditioning device or the like, no satisfactory control can be attained yet.
That is, the flow rate of the supplied air may sometime be increased abruptly by the intrusion of a sudden wind through the gallery (suction port) of the air conditioning device for supplying conditioned air to the inside of the coating booth. Further, the air flow rate also varies due to the change in the air density depending on the temperature change in the preheating heater disposed in the air conditioning device or on the change in the pressure loss due to the increase or decrease in the flow rate of water jetted from a humidifying shower disposed in the air conditioning device. Furthermore, the stream of the conditioned air is disturbed upon contact with the flow velocity sensor used for measuring the flow velocity, falling to obtain exact detection for the flow velocity of the conditioned air.
In view of the above, the present inventors, et. al. have made various studies and experiments on the measurement of the flow velocity of air supplied to the coating booth and on the control of the air supply blower and, as a result, found that signals obtained from the continuous measurement for the flow velocity of air supplied by the flow velocity sensors often contain primary variations fluctuating at relatively short period, for example, about from 1 to 4 sec, which may be attributable to external disturbances such as the characteristics of the flow velocity sensor per sc and secondary variations external disturbances fluctuating at relatively longer period, for example, about from 10 to 30 sec, which may be attributable to the external disturbances such as atmospheric air drawn to the air conditioning device or the change in the operation states of warming and humidifying device, as well as that exact control is possible by controlling the air supply blower using the signals after removed with the primary and secondary variations caused by such external disturbances.